The ES5 Downloads page only has links for the most recent release of ES5, but it is easy to download previous versions. Find the link you would use on that page for your operating system. Notice that there are two places in the link that specify the version. For example, ES5.4.0 links have "5_4_0" in two places. Replace both instances of the current version in the link with the version you need. Most common back versions needed are 5_2_3, 5_3_2, and 5_3_3.